Control for sump pump

ABSTRACT

A control for a motor driving a sump pump having lower and upper limit probes which includes first and second silicon controlled rectifiers having electrodes which are coupled to the respective probes. The anode-cathode circuit of the second silicon controlled rectifier includes a lamp having an associated photocell. The photocell is connected to the control electrode of a bilateral solid state switch, or triac, which is in series with the motor. The first silicon controlled rectifier is supplied with half-waves of a-c. so that it conducts when the lower limit probe is submerged, but is non-latching. Responsive to such conduction is a capacitor which applies direct voltage to the second silicon controlled rectifier so that the latter latches on when the upper probe becomes submerged. Thus when the water in the sump is pumped down, out of contact with the upper limit probe, the motor continues to be energized. However, when the water is pumped below the level of the lower limit probe, the first silicon controlled rectifier becomes non-conducting and the capacitor no longer applies direct voltage to the second silicon controlled rectifier so that the latter becomes unlatched, thereby turning off the motor. The silicon controlled rectifiers are supplied with current from an isolated secondary winding and the circuit is further isolated from the motor by lamp and photocell.

United States Patent I Quinn 1 May 30, 1972 [s41 CONTROL Fon SUMP PUMPJames L. Quinn, 6143 West Touhy Avenue, Chicago, 111. 60648 22 Filed:Sept.2, 1970 [21] Appl.No.: 68,940

[72] Inventor:

[52] U.S. Cl. ..318/482, 417/36 Perren ....318/482 Jones ..417/45Primary Examiner-Barnard A. Gilheany Assistant Examiner-Thomas Langer IAttorney-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[ 571 ABSTRACT A control for a motor driving a sump pump having lowerand upper limit probes which includes first and second siliconcontrolled rectifiers having electrodes which are coupled to therespective probes. The anode-cathode circuit of the second siliconcontrolled rectifier includes a lamp having an associated photocell. Thephotocell is connected to the control electrode of a bilateral solidstate switch, or triac, which is in series with the motor. The firstsilicon controlled rectifier is supplied with half-waves of a-c. so thatit conducts when the lower limit probe is submerged, but isnon-latching. Responsive to such conduction is a capacitor which appliesdirect voltage to the second silicon controlled rectifier so that thelatter latches on when the upper probe becomes submerged.

Thus when the water in the sump is pumped down, out of contact with theupper limit probe, the motor continues to be energized. However, whenthe water is pumped below the level of the lower limit probe, the firstsilicon controlled rectifier becomes non-conducting and the capacitor nolonger applies direct voltage to the second silicon controlled rectifierso that the latter becomes unlatched, thereby turning off the motor. Thesilicon controlled rectifiers are supplied with current from an isolatedsecondary winding and the circuit is further isolated from the motor bylamp and photocell.

7 Claims, 4 Drawing figures Lowenumr PROBE. B

CONTROL FOR SUMP PUMP It is an object of the present invention toprovide a novel solid state control for a sump pump or the like whichhas greater reliability than the usual control employing floatoperatedlimit switches, or employing electro-mechanical relays, and in whichreliability is not afiected even when the system must stand dormant forextended periods. It is another object to provide a solid state controlfor a sump pump which draws practically no current as long as the waterin the sump is at a low level, which employs only low values of controlcurrent when the probes are successively submerged and in which theprobes operate free of electrolytic effects.

It is a related object of the invention to provide a solid state controlcircuit which is electrically isolated at both its input and at itsoutput from the regular a-c. supply line with an independent groundcircuit for providing a reference voltage level for the probes. It ismore specifically an object of the invention to provide a solid statecontrol circuit in which isolation is provided at the input by means ofa transformer and in which isolation is provided at the output by meansof a lampphotocell stage, with the photocell serving to actuate thecontrol electrode of a triac or similar bilateral solid state switchwhich is connected in series with the pump motor.

It is a general object of the present invention to provide a solid statecontrol circuit, as above, which is economical, highlycompact, and whichis entirely self-contained, intended for mounting well above the waterlevel to facilitate quick and easy installation and prompt substitutionin the event any servicing becomes necessary.

Other objects and advantages of the invention will become apparent uponreading the attached detailed description and upon reference to thedrawings in which:

FIG. 1 is a crosssectional diagram of a typical installation employingthe present invention;

FIG. 2 is an enlarged elevational view of one of the probes;

FIG. 3 is a bottom view of the probe shown in FIG. 2;

F IG. 4 is a schematic diagram of the control circuit.

While the invention has been described in connection with a preferredembodiment, it will be understood that I do not intend to be limited tothe particular embodiment shown, but I intend, on the contrary, to coverthe various alternative and equivalent constructions included within thespirit and scop of the appended claims.

Turning now to FIG. 1 there is disclosed a typical installationincluding a sump pump assembly made up of a motor M and centrifugal pumpP mounted in a sump S and having a vertical discharge pipe 11 includingthe usual check valve 12. Secured to the pipe 11, or otherwise mountedwell above the level of the water and separate from the motor and pump,is a control unit 15 having a lower limit probe 16 and an upper limitprobe 17 connected to the control unit by insulated wires 18, 19respectively. Each probe 16, 17 is preferably mounted on a friction-typeclamp or slide 20 (see FIGS. 2 and 3), made of springy plastic or otherinsulating material permitting easy adjustment of the lower and upperprobe positions. The electrode material is preferably carbon, a shortlength of carbon rod being imbedded in the plastic with only the lowertip exposed. It is one of the features of the construction that, exceptfor the probes, the unit 15 is entirely self-contained, the housing 15including a socket 21 for plugging in a cord 22 leading from the motor.The supply cord 23 may be plugged into any convenient a-c. outlet.

While the operating sequence will be discussed in greater detail it willsufiice for the present to say that when the level of the water in thesump reaches the upper probe 17 the motor is actuated and remainsenergized until the water is pumped down to below the level of the lowerprobe 16, whereupon the motor is turned off. This insures that the waterwill not rise any higher than the upper probe, and the cycle time may bemade either long or short by varying the amount by which the lower probeis spaced downwardly from the upper probe.

In accordance with the present invention, a first solid state switch isprovided having a control element, or gate, connected to the lower probeand supplied with half-waves of current, so that the load currentcyclically passes through zero, so as to be non-latching. At the outputof the first solid state switch is a capacitor which is charged when thefirst switch is turned on and which serves to apply direct voltage to asecond solid state switch, the gate of which is connected to the upperprobe, the second solid state switch being latchable by reason of thedirect voltage so that it remains turned on, for sustained operation ofthe motor, until the first solid state switch turns off. Further inaccordance with the invention, both the input and output of the controlcircuit are isolated from the regular a-c. line, the control circuitbeing provided with its own ground connection which serves as areference for the probes.

Thus, referring to FIG. 4 of the drawings, a transformer 30 is providedhaving a primary winding 31 and a secondary winding 32, the latterhaving end terminals 33, 34 and a center tap 35. Forwardly facing diodes36, 37 perform full wave rectification to apply successive half-waves ofpositive voltage to line 38, withretum via line 39 connected to thecenter tap.

For the purpose of converting the rectified half-waves of voltage, whichcyclically pass through zero, to a direct voltage which does not passthrough zero, so as to provide latching in the next switching stage, afirst solid state switch 40 is provided having an anode 41, a cathode 42and a control electrode or gate 43, a capacitor 45 being connected tothe anode. The control electrode.43 is coupled to the lower probe 16 viaa resistor network, or divider, made up of a first resistor 46 which isconnected to the probe and a second resistor 47 which is connected,alongwith the cathode 43, to the return line 39 leading to the transformer.The solid state switch 40 is preferably in the form of a siliconcontrolled rectifier. Such a device is generally considered to belatchable, that is, to have the ability of remaining turned on, withcurrent flow in the anode-cathode circuit, once a pulse ofpositivetriggering voltage has been applied to the gate electrode.However, in the present instance latching is defeated by the fact thatthe load circuit is supplied with half-waves of a-c. A ground connection49 is made to the terminal 33 of the transformer for the purpose ofproviding a reference for the probe 16. Thus, in operation, when theprobe 16 is contacted by the water in the sump, the probe is effectivelyconnected to terminal 33 of the transformer where it is subjected to thepositive pulses which are in phase with the pulses of voltage applied tothe anode-cathode circuit, thereby making the switch conductive so thata For the purpose of turning on the motor when the water level reachesthe upper probe 17, and for latching in response to the direct voltageon capacitor 45, a second, or latchable, solid state switch in the formof a silicon controlled rectifier 50 is provided having an anode 51, acathode 52 and a control element or gate 53. The cathode terminal 52 ispreferably connected to a terminal 54 between the switch 40 and thecapacitor 45 so as to be directly subject to the direct voltage on thecapacitor and efi'ectively in series with the switch 40. The gateelectrode is connected to the midpoint of a network made up of a firstresistor 56 which leads to the upper probe and a second resistor 57which is connected to the cathode.

In order to couple the anode-cathode circuit of the switch 50 to themotor M a solid state relay is provided which is responsive to the loadcurrent of the switch but which nevertheless provides electricalisolation. Thus the motor is connected in the load circuitof a bilateralsolid state switch, or triac, 60, having load terminals 61, 62 and agate terminal 63. To energize the gate terminal 63, and to provide thedesired isolation, a lamp-photocell stage 70 is provided in series withthe output of the switch 50. The stage has a lamp 71 with a photocell,72 closely coupled thereto, the photocell being of the type whichsuffers a substantial reduction in resistance upon being light struck,thereby effectively connecting the gate terminal 63 to the upperterminal 61 of the triac to make the latter bi-directionally conductive.To insure that the tum-on voltage for the triac is at a reliably highlevel, in other words, to enable the triac to snap between its nonandconcharge, of the polarity shown, is built up upon the capacitor ductivemodes, a trigger diode 73 is interposed in series with the gate line 63.

While the operation of the overall circuit will be apparent to oneskilled in the art, it will be helpful to review a complete operatingcycle. It will be assumed first of all that the water level is initiallybelow the lower limit probe 16 as a result of a dry spell. Under suchcircumstances the switches 40, 50 and 60 are all turned off andsubstantially no current isdrawn from the supply line. When the waterlevel in the sump rises, due to rain or to any other cause, the contactof the water with the lower limit probe 16 effectively connects the gate43 to the transformer terminal 33, causing the switch 40 to conduct on anon-latching basis to charge the capacitor 45. This does not, however,result in turning on of the motor.

As the water continues to rise, reaching the level of the upper limitprobe 17, the gate 53 is effectively connected to the transformerterminal 33. The first positive half-wave from the terminal 33 triggersthe switch 50 for conduction, and conduction continues thereafter byreason of the fact that the charge on the capacitor 45 prevents thevoltage applied to the switch 50 from going through the zero axis.Conduction turns on the lamp 7] which drops the resistance of thephotocell 72. Any appreciable drop makes the trigger diode 73conductive, thereby turning on the triac 60 so that current may flow tothe motor from the supply line.

As the water level drops away from the upper limit probe the circuit tothe gate 53 is broken but the switch 50 continues to conduct by reasonof the direct voltage existing across the capacitor 45. However, as thewater level drops still further, finally clearing the lower limit probe16, the switch 40, which operates in a non-latching mode, is effectivelyturned ofl so that the capacitor 41 is no longer maintained in thecharged condition. The charge accumulated in the capacitor is quicklydrained off by the load circuit so that the voltage on the capacitorbecomes zero and conduction through the switch 50 ceases, turning offthe lamp 71. This causes the resistance of the photocell 72 to quicklyrise to the point where the voltage across the trigger diode 73 is nolonger adequate to produce current flow thereby making the triac 60non-conductive, turning off the motor. The motor remains'off until thewater level again rises to produce successive contact with the probesl6, l7, and the cycle is repeated.

Typical parameters which may be employed in a practical circuit are asfollows:

transformer 30 18 volts r.m.s.,

center tapped The resistors 46, 47 and 56, 57 may be adjusted relativeto one another to provide the desired degree of sensitivity and so thatthe gate electrodes are not triggered by presence of foam on the waterin the sump. Use of a triac type SC 51B pen-nits a pump motor on theorder of one-half horsepower to be employed. By using one of thetransformer terminals as a reference ground connection, the voltage onthe probes is purely alternating, thereby to minimize corrosion orplating effects and insuring a long probe life. It will be apparent,however, to one skilled in the art that the reference ground connectionmay, if desired, be made to the positive voltage line 38. This changewould enable the switch 40 to conduct during successive half cyclesrather than in alternate half cycles and would be feasible with somesacrifice in probe life or where probes of a noble metal such asplatinum are used. For reasons of cost it is desirable to use carbon asa probe material.

It will also be apparent to one skilled in that art that while full waverectification by diodes 36, 37 is preferred, one-half of the transformersecondary, and one diode, may, ifdesired, be dispensed with to obtainhalf-wave rectification. Indeed, becauseof the rectification which isinherent in the switches 40, it is not essential to employ a rectifierin the voltage supply. Thus the term "half-waves of a-c." as used hereinincludes half-waves in a fully rectified series, in a half-waverectified series, or in a non-rectified wave.

In the preferred form of circuit the switches 40, 50 are effectivelyconnected in series with one another. This insures that when the waterlevel drops below the lower limit probe the lamp 71 in the load circuitof switch 50 is "doubly" turned off, that is, turned off by lack of gatecurrent and turned off by lack of current supply to the anode-cathodecircuit. However, it will be understood that it is not essential toconnect the switches 40, 50 in series and that the cathode return leadof the switch lead, may, if desired, be connected to the transformerreturn line 39 without departing from the invention.

The term direct voltage", particularly referring to the voltageappearing across the capacitor 45, is intended to mean a voltage whichdoes not drop to zero level but has a net value at all times, eventhough subject to considerable cyclical variation in level.

Since the probes, by reason of the ground connection 49, are suppliedwith substantially pure a-c., they are electrolytically neutral even inwater having a high ion content. Both the plating" which would tend tooccur where the probes having net negative potential or the loss bycorrosion which would tend to occur where the probes have a net positivepotential are effectively defeated. Nor is it possible for the probes tobe affected by leakage currents because of the high degree of electricalisolation provided in the transformer and lampphotocell stage.

It is preferred to employ, in the position of the switch 40, a siliconcontrolled rectifier which is capable of latching and to operate theswitch in a non-latching mode. However it will be apparent to oneskilled in the art that non-latching type switches, such as a powertransistor, may be substituted, if desired, without departing from theinvention. Indeed, as far as the first switching stage is concerned, andin the broader aspects of the invention, any device may be employedwhich is of a non-latching nature and which is capable of producing adirect voltage at its output whenever the probe 16 is submerged forachieving a latched condition in the switch 50.

The present solid state control for sump motor overcomes I many of theproblems which have made conventional controls for a sump motor lessthan completely reliable. Thus the present system avoids the usualfloats, mechanical linkages and switch contacts which, in this type ofenvironment, tend to rust, corrode or malfunction, particularly after aperiod of inactivity. Electromechanical relays, with theirsusceptibility to dirt and corrosion have also been completely avoided.All control elements with the exception of the stationary probes l6, 17may be sealed in a compact, self-contained enclosure and may, ifdesired, be potted in epoxy resin or the like. The device 15 may bereadily detached and a replacement substituted within a few minutestime, or a new pump-motor assembly may be substituted, leaving thecontrol unit inplace. Moreover, by making the control system completelyindependent of the motor and pump, manufacture and installation of thelatter is greatly simplified.

I claim as my invention:

1. In a control for a motor driving a sump pump having associated lowerand upper limit probes and intended for operation from the regular a-c.supply line, the combination comprising a transformer having its primarywinding connected to the a-c. line and having a low voltage secondarywinding with an associated rectifier to serve as a source of rectifiedhalfwaves of alternating current, first and second silicon controlledrectifiers having anode-cathode circuits connected in series with oneanother across said source and having control electrodes coupled to therespective lower and upper limit probes, the side of the transformersecondary winding which is associated with the anode terminals beinggrounded so that the controlled rectifiers are successively conditionedfor conduction as the water rises to the level of the lower and upperlimit probes, means including a capacitor connected in the anode-cathodecircuit of the first controlled rectifier for applying direct voltage tothe anode-cathode circuit of the second controlled rectifier forlatching the same in the conductive state until such time as the waterlevel drops below the level of the lower limit probe, a lamp connectedin series with the anode-cathode circuit of the second controlledrectifier, a photocell close-coupled to the lamp so as to be responsiveto the illumination thereof, a bilateral solid state switch having aload circuit connected in series with the motor and supply line andhaving a control electrode coupled tothe photocell so that the motorremains turned on as long as current flows in the anode-cathode circuitof the second controlled rectifier.

2. In a control for a motor driving a sump pump having lower and upperlimit probes, the combination comprising a transformer source ofhalf-waves of a-c., a reference ground connection at the output side ofthe transformer, solid state switch having an anode-cathode circuit anda control electrode, a second solid state switch having an anode-cathodecircuit and a control electrode,.the anode-cathode circuits beingconnected in series with one another to the source of pulses, acapacitor connected in series with the anode-cathode circuit of thefirst switch and in parallel with the anode-cathode circuit of thesecond switch, the control electrode of the first switch being connectedto the lower limit probe so that when the lower limit probe is submergedhalf-waves of current flow through the first switch to charge thecapacitor, the second switch having a latching characteristic whenenergized by directvoltage and the control electrode of the secondswitch being connected to the upper limit probe so that when the upperlimit probe is submerged by rising of the water level in the sumplatched current flows through the second switch, and

isolating relay means responsive to current flow through the secondswitch for turning on the motor with the latter being monitored on byreason of the latching until the water level drops below the lower limitprobe. I

3. in a control for a motor driving a sump pump having lower and upperlimit probes, the combination comprising a transformer source ofrectified half-waves of a-c., a reference ground connection at theoutput side of the transformer, first and second solid state switcheshaving anode-cathode circuits connected to the source and the ground andhaving lower and upper control electrodes respectively connected to theprobes, a capacitor connected in the anode-cathode circuit of the firstswitch so that the capacitor is charged whenever the first probe issubmerged, means for applying direct voltage from the capacitor to theanode-cathode circuit of the second switch, the second switch having alatching characteristic when energized by direct voltage so that whenthe second probe is submerged by reason of a rise in the water level,latched current flows through the second switch, and relay meansresponsive to the current flow through the second switch butelectrically isolated therefrom for energizing the motor until thecapacitor is discharged by reasons of dropping of the water level belowthe lower limit probe.

4. in a control for a motor driving a sump pump having lower and upperlimit probes, the combination comprising a transformer source ofhalf-waves of a-c., a reference ground connection at the output side ofthe transformer, first and second silicon controlled rectifiers havingtheir anodecathode circuits connected to the source and having controlelectrodes respectively connected to the lower and upper probes, meansincluding a capacitive element for operatively coupling theanode-cathode circuit of said first silicon controlled rectifier to theanode-cathode circuit of said second silicon controlled rectifier sothat a rise in water level to the lower probe causes conduction in thefirst controlled rectifier for charging of the capacitor for applicationof direct voltage to the second controlled rectifier and a rise in waterlevel to the upper probe causes flow of current in the second controlledrectifier which is latchingly maintained until the water level dropsbelow the level of the lower probe, and solid state relay meansresponsive to flow of current in the second controlled rectifier butelectrically isolated therefrom for energizlower and upper limit probes,the combination comprising a source and having a control electrodeconnected to the upper probe, said switch having a latchingcharacteristic when its anode-cathode circuit is energized by anuninterrupted'forward biasing direct voltage, means including acapacitor coupled in series with the lower probe for applying anuninterrupted, forward biasing direct voltage component to theanode-cathode circuit of said switch as long as the lower probe issubmerged so that when the control electrode'is energized due to a risein water level to the upper probe the switch is latched on and continuesconduction until the water level drops below the lower probe despite thesubsequent de-energization of the control electrode associated with saidsolid state switch, and solid state relaymeans responsive to the flow ofcurrent in the anode-cathode circuit but electrically isolated therefromfor energizing the motor.

6. In a control for a motor driving a sump pump having lower and upperlimit probes, the combination comprising a transformer source ofhalf-waves of a-c., a reference ground connection at the output side ofthe transformer, a solid state switch having an anode-cathode circuitconnected to the source and having a control electrode connected to theupper limit probe, said switch having a latching characteristic when itsanode-cathode circuit is energized by an uninterrupted, forward biasingdirect voltage, a lamp connected in series with the anode-cathodecircuit, a photocell coupled to, the lamp, a bilateral solid stateswitch having a load circuit connected in series with the motor andhaving a control electrode coupled to the photocell for turning on themotor, and means including a capacitor coupled in series with the lowerlimit probe for applying an uninterrupted, forward biasing directvoltage to the anode-cathode circuit of said solid state switch to latchin the solid state switch for continued running of the motor, despitethe subsequent de-energization of the control electrode associated withsaid solid state switch, until the water drops below the lower limitprobe.

7. In a control for a motor driving a sump pumphaving associated lowerand upper limit probes and arranged for powering from the regular a-c.,power line, the combination comprising a transformer having its primaryconnected to the power line and having a low voltage secondary windingand an associated full-wave rectifier for providing a continuous trainof rectified half-waves of a-c., a solid state switch having ananode-cathode circuit connected to the source of rectified half-wavesand having a control electrode connected to the high limit probe, theswitch having a latching characteristic when its anode-cathode circuitis energized by an uninterrupted, forward biasing direct voltage, a lampconnected in series with the anode-cathode circuit, a photocell closelycoupled to the lamp but electrically isolated therefrom, a bilateralsolid state switch having a load circuit connected in series with themotor and having a control electrode connected to the photocell so thatwhen the water rises to the level of the upper limit probe conductionoccurs in the solid state switch, means in series with and controlled bythe lower limit probe for applying an uninterrupted, forward biasingdirect voltage to the anode-cathode circuit of the solid state switch aslong as the lower limit probe is submerged thereby to produce latchingof the solid state switch and continued running of the motor, despitethe subsequent de-energization of the control electrode associated withsaid solid state switch, until the water drops below the lower limitprobe whereupon the motor is turned off, the lower limit probe beingeffectively connected to one terminal of the secondary winding andanother terminal of the secondary winding being grounded so thatalternating voltage is conh'nuously applied to the lower limit probethereby to minimize electrolytic plating or corrosion of the lower limitprobe during sustained contact with the water in the sump.

I0! I! k l l

1. In a control for a motor driving a sump pump having associated lowerand upper limit probes and intended for operation from the regular a-c.supply line, the combination comprising a transformer having its primarywinding connected to the a-c. line and having a low voltage secondarywinding with an associated rectifier to serve as a source of rectifiedhalf-waves of alternating current, first and second silicon controlledrectifiers having anode-cathode circuits connected in series with oneanother across said source and having control electrodes coupled to therespective lower and upper limit probes, the side of the transformersecondary winding which is associated with the anode terminals beinggrounded so that the controlled rectifiers are successively conditionedfor conduction as the water rises to the level of the lower and upperlimit probes, means including a capacitor connected in the anode-cathodecircuit of the first controlled rectifier for applying direct voltage tothe anodecathode circuit of the second controlled rectifier for latchingthe same in the conductive state until such time as the water leveldrops below the level of the lower limit probe, a lamp connected inseries with the anode-cathode circuit of the second controlledrectifier, a photocell close-coupled to the lamp so as to be responsiveto the illumination thereof, a bilateral solid state switch having aload circuit connected in series with the motor and supply line andhaving a control electrode coupled to the photocell so that the motorremains turned on as long as current flows in the anode-cathode circuitof the second controlled rectifier.
 2. In a control for a motor drivinga sump pump having lower and upper limit probes, the combinationcomprising a transformer source of half-waves of a-c., a referenceground connection at the output side of the transformer, solid stateswitch having an anode-cathode circuit and a control electrode, a secondsolid state switch having an anode-cathode circuit and a controlelectrode, the anode-cathode circuits being connected in series with oneanother to the source of pulses, a capacitor connected in series withthe anode-cathode circuit of the first switch and in parallel with theanode-cathode circuit of the second switch, the control electrode of thefirst switch being connected to the lower limit probe so that when thelower limit probe is submerged half-waves of current flow through thefirst switch to charge the capacitor, the second switch having alatching characteristic when energized by direct voltage and the controlelectrode of the second switch being connected to the upper limit probeso that when the upper limit probe is submerged by rising of the waterlevel in the sump latched current flows through the second switch, andisolating relay means responsive to current flow through the secondswitch for turning on the motor with the latter being monitored on byreason of the latching until the water level drops below the lower limitprobe.
 3. In a control for a motor driving a sump pump having lower andupper limit probes, the combination comprising a transformer source ofrectified half-waves of a-c., a reference ground connection at theoutput side of the transformer, first and second solid state switcheshaving anode-cathode circuits connected to the source and the ground andhaving lower and upper control electrodes respectively connected to theprobes, a capacitor connected in the anode-cathode circuit of the firstswitch so that the capacitor is charged whenever the first probe issubmerged, means for applying direct voltage from the capacitor to theanode-cathode circuit of the second switch, the second switch having alatching characteristic when energized by direct voltage so that whenthe second probe is submerged by reason of a rise in the water level,latched current flows through the second switch, and relay meansresponsive to the current flow through the second switch butelectrically isolated therefrom for energizing the motor until thecapacitor is discharged by reasons of dropping of the water level belowthe lower limit probe.
 4. In a control for a motor driving a sump pumphaving lower and upper limit probes, the combination comprising atransformer source of half-waves of a-c., a reference ground connectionat the output side of the transformer, first and second siliconcontrolled rectifiers having their anode-cathode circuits connected tothe source and having control electrodes respectively connected to thelower and upper probes, means including a capacitive element foroperatively coupling the anode-cathode circuit of said first siliconcontrolled rectifier to the anode-cathode circuit of said second siliconcontrolled rectifier so that a rise in water level to the lower probecauses conduction in the first controlled rectifier for charging of thecapacitor for application of direct voltage to the second controlledrectifier and a rise in water level to the upper probe causes flow ofcurrent in the second controlled rectifier which is latchinglymaintained until the water level drops below the level of the lowerprobe, and solid state relay means responsive to flow of current in thesecond controlled rectifier but electrically isolated therefrom forenergizing the motor.
 5. In a control for a motor driving a sump pumphaving lower and uPper limit probes, the combination comprising atransformer source of half-waves of a-c., a reference ground connectionat the output side of the transformer, a solid state switch having ananode-cathode circuit connected to the source and having a controlelectrode connected to the upper probe, said switch having a latchingcharacteristic when its anode-cathode circuit is energized by anuninterrupted forward biasing direct voltage, means including acapacitor coupled in series with the lower probe for applying anuninterrupted, forward biasing direct voltage component to theanode-cathode circuit of said switch as long as the lower probe issubmerged so that when the control electrode is energized due to a risein water level to the upper probe the switch is latched on and continuesconduction until the water level drops below the lower probe despite thesubsequent de-energization of the control electrode associated with saidsolid state switch, and solid state relay means responsive to the flowof current in the anode-cathode circuit but electrically isolatedtherefrom for energizing the motor.
 6. In a control for a motor drivinga sump pump having lower and upper limit probes, the combinationcomprising a transformer source of half-waves of a-c., a referenceground connection at the output side of the transformer, a solid stateswitch having an anode-cathode circuit connected to the source andhaving a control electrode connected to the upper limit probe, saidswitch having a latching characteristic when its anode-cathode circuitis energized by an uninterrupted, forward biasing direct voltage, a lampconnected in series with the anode-cathode circuit, a photocell coupledto the lamp, a bilateral solid state switch having a load circuitconnected in series with the motor and having a control electrodecoupled to the photocell for turning on the motor, and means including acapacitor coupled in series with the lower limit probe for applying anuninterrupted, forward biasing direct voltage to the anode-cathodecircuit of said solid state switch to latch in the solid state switchfor continued running of the motor, despite the subsequentde-energization of the control electrode associated with said solidstate switch, until the water drops below the lower limit probe.
 7. In acontrol for a motor driving a sump pump having associated lower andupper limit probes and arranged for powering from the regular a-c.,power line, the combination comprising a transformer having its primaryconnected to the power line and having a low voltage secondary windingand an associated full-wave rectifier for providing a continuous trainof rectified half-waves of a-c., a solid state switch having ananode-cathode circuit connected to the source of rectified half-wavesand having a control electrode connected to the high limit probe, theswitch having a latching characteristic when its anode-cathode circuitis energized by an uninterrupted, forward biasing direct voltage, a lampconnected in series with the anode-cathode circuit, a photocell closelycoupled to the lamp but electrically isolated therefrom, a bilateralsolid state switch having a load circuit connected in series with themotor and having a control electrode connected to the photocell so thatwhen the water rises to the level of the upper limit probe conductionoccurs in the solid state switch, means in series with and controlled bythe lower limit probe for applying an uninterrupted, forward biasingdirect voltage to the anode-cathode circuit of the solid state switch aslong as the lower limit probe is submerged thereby to produce latchingof the solid state switch and continued running of the motor, despitethe subsequent de-energization of the control electrode associated withsaid solid state switch, until the water drops below the lower limitprobe whereupon the motor is turned off, the lower limit probe beingeffectively connected to one terminal of the secondary winding andanother terminal of the secondary winding being grounded so thatalternating voltage is continuously applied to the lower limit probethereby to minimize electrolytic plating or corrosion of the lower limitprobe during sustained contact with the water in the sump.